Significance: The function of osteocytes and how mechanical strain is translated into biological signals[unreadable] from these cells is unknown. Identification of osteocyte specific proteins that are regulated by mechanical[unreadable] strain and determination of their function should provide significant information regarding the role of[unreadable] osteocytes in the regulation of bone mass. Only recently have osteocyte specific proteins been identified.[unreadable] One of these proteins, called E11, is specifically expressed in the early osteocyte as it is embedding in[unreadable] osteoid and appears to play a role in the generation of dendritic processes. E11 may be essential for[unreadable] osteocyte communication and osteocyte viability. Our hypothesis is that the E11 antigen is responsible for[unreadable] dendrite formation in osteocytes, that allows osteocytes to become embedded in osteoid in a manner to[unreadable] support communication between osteocytes and with cells on the bone surface. Approach: The specific[unreadable] aims for this project are 1). Determine the role of E11 in dendrite formation, osteocyte communication and[unreadable] osteocyte viability, 2). Determine the effects of mechanical loading on E11 expression, and 3). Determine the[unreadable] mechanism of action of E11 through its associations with extra and intracellular molecules known to regulate[unreadable] the cytoskeleton. Cell lines and primary cells overexpressing or underexpressing E11 will be subjected to[unreadable] shear stress to determine effects on gap junctions and hemichannels, major means by which osteocytes[unreadable] communicate. Transgenic mice lacking E11 in osteocytes and mice with reporter molecules driven by the[unreadable] E11 promoter will be subjected to loading and unloading. Innovation: Novel approaches to answer these[unreadable] questions include the use of an osteocyte-like cell line, targeted deletion of genes in osteocytes in vivo, use[unreadable] of endogenous E11 promoter driving a reporter gene for determination of response to loading and unloading,[unreadable] use of siRNA, and the investigation of hemichannels, a novel means by which osteocytes communicate.[unreadable] Therefore we will be able to alternate between in vitro and in vivo approaches for discovery and validation.[unreadable] Investigators and Environment: This project will be conducted as a collaboration between investigators[unreadable] with diverse expertise in academic environments possessing state of the art technology to address the[unreadable] questions posed in this application. Knowledge gained will be applied to the prevention and treatment of[unreadable] bone loss due to immobilization, space flight, microdamage, and disease states such as osteoporosis.